1. Field of the Invention
This invention relates to card cages for mounting circuit boards and more particularly to an improved card cage and grille structure for mounting such circuit boards.
2. Description of Related Art
Card cages, or racks, for mounting printed circuit boards that connect with other circuit boards and electronic components as part of an electronic system are known. They comprise generally a rectangular frame structure forming an enclosure for receiving circuit boards with end panels secured or securable at open ends of the frame. Generally, a rear panel connects to the frame. This rear panel is often referred to as a back plane connector, because it generally provides for the electrical connection between electronic components on circuit boards disposed within the frame and other electronic components forming an electronic system, such as a computer system. Some card cages employ a repositionable front plate or panel in place of such a back panel for making such electrical connections.
The rectangular frame structure of such racks usually include spaced side panels that extend generally parallel with the circuit boards, and opposed, transverse panels that extend between the side panels and generally transverse with respect to both the boards and the side panels. The racks also include guide members for receiving and supporting the circuit boards that are generally secured to or formed integrally with the transverse panels. The transverse panels frequently include apertures between the guides so that they form a grille structure that supports the circuit boards and allows cooling air to pass over the boards.
The following United States Letters Patent disclose racks for mounting circuit boards having board supporting panels:
U.S. Pat. No. 4,519,016 (1985) to Bradley et al. discloses a card cage for mounting printed circuit boards in a stacked relationship with an intermediate frame member in a plane parallel with an upper and bottom frame member. The intermediate frame comprises a single piece of sheet metal with air openings that are punched or stamped pressed through the metal. Guides in the intermediate frame member are then formed by bending portions of the metal in the air openings in an appropriate direction to support circuit boards in both upper and lower frame members to provide a two level rack for mounting circuit boards. The metal working steps required to form guides limits each guide to specific applications and requires significant tooling changes for minor changes, such as the reduction or increase in the numbers of boards to be supported. Additionally, the guides formed by this process are not continuous; that is, the guides only engage a circuit board at a few widely spaced locations.
U.S. Pat. No. 4,583,149 (1986) to Ohlenburger discloses a rack for mounting printed circuit boards. A metal block contacts a heat conducting layer overlying the board. The block or metal components attached to the block provide a metal-to-metal contact with a metal portion of the housing to improve heat transfer from the circuit boards disposed in the rack.
U.S. Pat. No. 4,862,320 (1989) Schmidt et al. discloses a rack for mounting circuit boards that comprises a back panel for electrically engaging boards positioned in the rack. Metal side panels support molded plastic grilles at the top and bottom of the rack. Similarly, U.S. Pat. No. 5,024,627 (1991) Bennett et al. and U.S. Pat. No. 5,030,108 (1991) to Babow et al. disclose a card cage having a general frame structure with guide rails that are formed integrally with the upper frame structure of the cage.
U.S. Pat. No. 5,032,954 (1991) to Juza discloses a housing for electronic components that includes an extruded aluminum, tubular midsection, a front panel, and a die-cast double-domed rear wall. The tubular frame section comprises a single solid piece with no aperture therethrough. It does include integral guides for receiving circuit board edges and grooves for receiving screws to enable attachment of the front panel and the rear panel to form an enclosed card cage. Thus, this patent discloses a one piece, extruded metal, tubular frame with integrally formed lateral panels and board supporting panels. The board receiving aperture formed by the frame is fixed and can receive only a specific number of boards corresponding to the number of guides of a predetermined height corresponding to the orientation of the boards in the card cage. To enable such a card cage to support larger boards or larger numbers of boards requires making a new extrusion fixture.
U.S. Pat. No. 5,057,968 (1991) to Morrison discloses a rack for mounting circuit boards with metal guides that comprise blocks with machined passageways for conducting cooling liquid therethrough. The blocks are individual units that are brazed to form a cooling loop therein. Each guide must be individually formed by brazing blocks together to form the unitary panel. This structure does not provide any capability for air cooling of the components it supports.
U.S. Pat. No. 5,103,378 (1992) to Stowers et al. discloses an enclosure for receiving a card cage for holding circuit cards. A front panel connects to the cards in a commercially available card cage for holding a plurality of printed circuit boards as part of an interchangeable test adaptor.
U.S. Pat. No. 5,210,680 (1993) to Scheibler discloses a card cage having an air cooling system. The card cage comprises a housing having a fan in the bottom, a baffle plate supported above the fan by legs, and guide rails supported on rails respectively. Alternatively, the rails can support a series of baffle plates. The top of the housing includes similar rails supporting counter facing guide rails for supporting circuit boards.
As each of these and other card cages have been developed, a series of desirable features and characteristics have evolved for commercially acceptable card cages. For example, card cages, including the board supporting structures, preferably comprise a relatively strong, durable materials so as to be rugged and reliable in use and suited for a variety of environments. These structures should promote heat dissipation from the circuit boards and electronic components positioned thereon. They should provide adequate support and guidance to circuit boards inserted in the card cage. Additionally, the card cages should be relatively inexpensive to build, maintain and replace.
Likewise, a number of like criteria for the grille structures have developed. Specifically, grille structures should also be formed of a relatively strong materials, facilitate cooling air flow past the circuit boards and provide integrally formed guides for receiving the circuit boards. Advantageously, the grille structures should be formed for use in multiple applications as needed without requiring special tooling or different machinery to reduce the cost of manufacturing such grille structures also well as reduce inventory requirements.
None of the card cages or the grille structures of the prior art satisfy all of these requirements. For example, the commercially available card cages generally have injection molded card guides. Some do have metal portions including grille structures and slots for guiding and supporting circuit boards. However, these structures generally comprise preformed bent sheet metal structures that are constructed for a specific application. Thus, any change in an application requires the use of different tools and/or machines to provide a card cage with such grilles. The Juza patent discloses an extruded frame structure formed as a single tubular piece. In applications that require the housing of boards with greater heights than the card cage or a greater number of boards than the preformed grooves of the card cage require a new part with the associated re-tooling that includes a new extrusion die, and other modifications that can increase production costs significantly.
Card cages for mounting electronic circuit boards have certain common characteristics. Each includes a frame structure generally defining a back plate for electrically connecting with the components on the circuit boards, side panels arranged in a generally parallel fashion with the boards positioned in the cage, and top and bottom members or grilles for supporting guides for receiving and supporting circuit boards in the card gage. Each of the top and bottom members may be provided with cooling passages therein for promoting dissipation of heat generated by the electronic components of the circuit boards positioned in the card cage. However, the size of circuit boards that are mountable in such card cages are variable as are the number of circuit boards that may be used in a particular configuration. Consequently, each application for standard card cages require a separate grille if either or both the number of boards to be supported is different or the length of the boards is different.